The present invention relates to a microwave plasma CVD apparatus in which microwave is supplied into an applicator, plasma of reaction gas (for example, mixed gas of hydrogen and hydrocarbon, mixed gas of silane and nitrogen, or the like) is generated in a bell jar provided in the applicator, and a sample is exposed in the plasma atmosphere for a long time to deposit material such as diamond on the surface of the sample.
FIGS. 5 and 6 show the structure of an example of a conventional microwave plasma CVD apparatus.
FIG. 5 is an explanatory view showing the structure of the apparatus shown from a microwave travel direction. FIG. 6 is an explanatory view of the same shown from a direction perpendicular to the microwave travel direction. In the drawings, numeral 101 is an applicator allowing microwaves to enter therein from a plurality of directions, numeral 102 is a bell jar, numeral 103 is a circular sample such as a silicon wafer, and numeral 104 is a rotary sample-receiving table. The rotary sample-receiving table 104 is arranged in the bell jar 102 comprising a silica tube provided in the applicator 101. The applicator 101 is composed of walls fixed by the welding or the like.
In using the above apparatus, the inner pressure of the bell jar 102 is set at about 10.sup.-5 Torr by exhaust, and a mixed gas of, for example, hydrogen and hydrocarbon or carbon dioxide is charged into the bell jar 102 to a pressure of about 10 to 40 Torr. Then, microwave is supplied into the applicator 101 to generate plasma of the mixed gas in the bell jar 102.
FIGS. 7 and 8 show distribution of plasma intensity in the plasma CVD apparatus shown in FIG. 6 along the microwave travel direction. In the drawings, numeral 107 is plasma. When the sample 103 is placed on the sample-receiving table 104 and the table 104 is rotated in order to expose the sample 103 in the plasma atmosphere, material such as diamond is deposited on the surface of the sample 103.
In the conventional plasma CVD apparatus, however, the applicator is composed of walls (ceiling and side walls) fixed by the welding as stated above to form a rectangular space, so that only plasma having a single intensity distribution is generated. When a film is formed on the sample 103 under this distribution of plasma, since the sample 103 is rotated about the center of the table 104 so that exposure time of a peripheral portion of the sample 103 in the plasma atmosphere is shorter than that of a central portion thereof, film thickness of the peripheral portion becomes thinner than that of the central portion. Accordingly, there has been a problem that the conventional plasma CVD apparatus cannot make samples with uniform film thickness.
The present invention was made to solve the above problem, and it is an object of the present invention to provide a microwave plasma CVD apparatus capable of uniformly depositing material on a sample by continuously changing the distribution of plasma intensity.